In U.S. Pat. No. 5,083,887 to Dotany, there is illustrated and described an end mill with one or more helical arrays of radially mounted quadrilateral cutting inserts. Along each helical array, the cutting inserts are so disposed that a radially directed upper edge of a cutting insert overlaps a radially directed upper edge of an adjacent cutting insert whilst their operative cutting edges axially overlap to constitute a fully effective cutting edge during a cutting operation.
End mills of this type require that a cutting insert's lower surface is clear of an inner upper insert corner remote from its adjacent cutting insert's operative cutting edge. Thus, in an exemplary right hand end mill having cutting inserts stepping up along a left hand helix shown in FIGS. 1 and 2 corresponding to FIGS. 1 and 3 of US '887, a cutting insert's lower surface clears the inner upper insert corner remote from the trailing end of its adjacent cutting insert's operative cutting edge.
This limiting feature in an end mill having a relatively small diameter or adapted for use with cutting inserts whose dimensions are relatively large relative to its diameter results in a large insert to insert angular pitch denoted A in FIG. 2 causing inter alia noisy and interrupted cutting.